MAX1291 Datasheet, PDF (15/20 Pages) Maxim Integrated Products – 250ksps, +3V, 8-/4-Channel, 12-Bit ADCs with +2.5V Reference and Parallel Interface

250ksps, +3V, 8-/4-Channel, 12-Bit ADCs
with +2.5V Reference and Parallel Interface
Table 4. Channel Selection for Pseudo-Differential Operation (SGL/DIF = 0)
A2
A1
A0
CH0
CH1
CH2
CH3
CH4*
CH5*
CH6*
0
0
0
+
-
0
0
1
-
+
0
1
0
+
-
0
1
1
-
+
1
0
0
+
-
1
0
1
-
+
1
1
0
+
1
1
1
-
*Channels CH4–CH7 apply to MAX1291 only.
CH7*
-
+
Applications Information
Power-On Reset
When power is first applied, internal power-on reset cir-
cuitry activates the MAX1291/MAX1293 in external
clock mode and sets INT high. After the power supplies
stabilize, the internal reset time is 10µs, and no conver-
sions should be attempted during this phase. When
using the internal reference, 500µs is required for V_REF
to stabilize.
Internal and External Reference
The MAX1291/MAX1293 can be used with an internal
or external reference voltage. An external reference
can be connected directly to REF or REFADJ.
An internal buffer is designed to provide +2.5V at REF for
the both the MAX1291 and the MAX1293. The internally
trimmed +1.22V reference is buffered with a +2.05V/V
gain.
Table 5. Data-Bus Output (8+4 Parallel
Interface)
PIN HBEN = 0
HBEN = 1
D0 BIT 0 (LSB)
BIT 8
D1
BIT 1
BIT 9
D2
BIT 2
BIT 10
D3
BIT 3
BIT 11 (MSB)
D4
BIT 4
BIPOLAR
(UNI/BIP = 0)
UNIPOLAR
(UNI/BIP = 1)
BIT 11
0
D5
BIT 5
BIT 11
0
D6
BIT 6
BIT 11
0
D7
BIT 7
BIT 11
0
Internal Reference
With the internal reference, the full-scale range is +2.5V
with unipolar inputs and ±1.25V with bipolar inputs. The
internal reference buffer allows for small adjustments
(±100mV) in the reference voltage. See Figure 7.
Note that the reference buffer must be compensated
with an external capacitor (4.7µF min) connected
between REF and GND to reduce reference noise and
switching spikes from the ADC. To further minimize
noise on the reference, connect a 0.01µF capacitor
between REFADJ and GND.
External Reference
With both the MAX1291 and MAX1293, an external ref-
erence can be placed at either the input (REFADJ) or
the output (REF) of the internal reference buffer amplifier.
Using the REFADJ input makes buffering the external
reference unnecessary. The REFADJ input impedance
is typically 17kΩ.
+3V
50k
330k
50k
GND
0.01µF
GND
4.7µF
MAX1291
MAX1293
REFADJ
REF
Figure 7. Reference Voltage Adjustment with External
Potentiometer
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